I
noun
BAD : Remember to call me if you need a help.
GOOD : Remember to call me if you need help.
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Help is usually an uncountable noun: 'Do you want some help?' 'He doesn't like asking for help.'
Note however the phrase be a (great/tremendous) help : 'Thanks for coming and looking after the children. You've been a great help.' 'It would be a great help if you could just address all the envelopes.'
II
verb
BAD : The girl's parents couldn't help to worry about her.
GOOD : The girl's parents couldn't help worrying about her.
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can't/couldn't help doing sth : 'I couldn't help laughing when I saw what he was doing.'